Codeforces Round #315 (Div. 2)

A. Music

B. Inventory

C. Primes or Palindromes?

/**
A. Music 
*/
#include<algorithm>
#include<iostream>
#include<cstring>
#include<cstdio>
#define maxn 100005
using namespace std;
int main(){
    int n,m,q;
    while(cin>>n>>m>>q){
        int ans=0;
        while(m<n){
            m+=(q-1)*m;
            ans++;
        }
        printf("%d\n",ans);
    }
    return 0;
}

/**
B. Inventory
*/
#include<algorithm>
#include<iostream>
#include<cstring>
#include<cstdio>
#define maxn 100005
using namespace std;
int a[maxn];
int ans[maxn];
bool b[maxn];
int main(){
    int n;
    while(~scanf("%d",&n)){
        memset(b,0,sizeof(b));
        memset(ans,0,sizeof(ans));
        for(int i=0;i<n;i++){
            scanf("%d",&a[i]);
            if(!b[a[i]]&&a[i]<=n)
                ans[i]=a[i];
            b[a[i]]=true;
        }
        int A=1;
        for(int i=0;i<n;i++){
            if(ans[i]) continue;
            while(b[A]) A++;
            ans[i]=A++;
        }
        for(int i=0;i<n;i++){
            if(i==0) printf("%d",ans[i]);
            else printf(" %d",ans[i]);
        }
        printf("\n");
    }
    return 0;
}

</pre><pre name="code" class="cpp">/**
C. Primes or Palindromes?
*/

#include<algorithm>
#include<iostream>
#include<cstring>
#include<cstdio>
#define maxn 1200005
#define ret 1.0*pr[i]/pa[i]
using namespace std;
int a[10];
bool check(int num){//判斷迴文數
    int A=0;
    while(num){
        a[A++]=num%10;
        num/=10;
    }
    for(int i=0;i<A/2;i++)
        if(a[i]!=a[A-i-1]) return false;
    return true;
}
int pa[maxn]={0};
int pr[maxn]={0};
bool b[maxn]={0};
void Init(){
    for(int i=2;i*i<=maxn-5;i++){
        if(!b[i]);
        for(int j=i+i;j<=maxn-5;j+=i)
            b[j]=true;
    }
    pa[1]=1;
    for(int i=2;i<=maxn-5;i++){
        pa[i]=pa[i-1]+check(i);
        pr[i]=pr[i-1]+(!b[i]);
    }
}
int main(){
    Init();
    double p,q;
    while(cin>>p>>q){
        p/=q;
        int ans=1;
        for(int i=2;i<=maxn-5;i++)//暴力求解
            if(ret<=p) ans=i;
        printf("%d\n",ans);
    }
    return 0;
}